Excellent lens
I have owned the lens for almost 3 years. I has performed admirably and has done everything that I have asked it to do. When used within its design range, you cannot have a better partner waiting on you to call it into action.
I have never been disappointed with it.
Some comment that it is heavy. It is only 8 oz. heavier that the 70-200 F2.8 and no one complains about that one.
I have carried it afield on numerous occasions and have not been made weary from the weight. Overall, an excellent addition to the photo equipment bag. I probably use it for 85% of my shooting.
May 6, 2014

Ballanced
PROs
if you only want to bring one lens
28mm to 300 mm
Quality built
CONs
Heavy
picture quality is not as good as the 70-200
Need to be at high aperture settings to get a good DOF
The cons are mitigated when you unexpectedly needed that 300mm with no time to spare and in the next moment you are needing the 28mm.
April 30, 2014

Totally Satisfied
I have been a pro since 1981. I have used 35mm, 2 1/4 square, and 4x5 in studio and on location. This lens is the one I use almost every time I shoot. I have the 16x35 2.8 and the 50 1.2 and I love them both, but when I am shooting sessions or weddings... this is the lens that I use almost exclusively. I have two 5D Mk2 bodies and the 28-300mm lens stays on one of them all the time. The clarity, color, sharpness, contrast, image stabilization, ease of use, durability... I could go on and on... this system replaces my medium format with six lenses and surpasses it... And the seamless use with my professional editing software that recognizes the lens with lens calibration is awesome... I could not be more pleased after almost three years of continuous use...
June 11, 2013

My GoTo Lens
As the title suggests, this is my GoTo lens. I currently carry a 10-22mm W/A, 28-135mm standard, and 100mm macro along with this lens. 9-times out of 10, the 28 to 300mm is on my 7D camera body. The pictures are sharp. I was at Hearst Castle and in-doors where flash photography isn't allowed and blown away with the quality of the pictures I ended up with, even in the dark theater room. The focus is fast and true. The colors are brilliant. I have a picture of a friend where I'm 50ft away and I took a headshot of him. Once back at home, I cropped it down to just his eyes and you can clearly see the reflection of Yellowstone National Park in his sunglasses. I love this camera and lens. The only drawbacks I see are that Canon says you can't use the extenders on it (I'd love to use a 2x extender) and the lens weight can be a drag if you have the camera on your neck for several hours.
May 26, 2013